Fractional-N synthesizer VCO coarse tuning

Abstract

Adjusting a voltage-controlled oscillator (VCO) accurately and reliably. The voltage-controlled oscillator VCO attempts to generate an output signal with a programmed known frequency. An ALC circuit and a VCTA circuit adjust the VCO's amplitude and frequency. The system alternates making changes between amplitude or frequency, checking at each change what (difficult-to-predict) effect this has had on the output of the VCO. Each time the VCO switched capacitor array setting is changed, a circuit reviews the VCO output, and determines whether the VCO output should be adjusted in amplitude and frequency. The VCO amplitude and the VCO frequency are adjusted in alternating steps, that is, adjusting the VCO frequency, determining if further adjustments are desired, adjusting the VCO amplitude, determining if further adjustments are desired, and repeating until the VCO coarse adjustment has been sufficiently conducted.

The invention claimed is: 
     
       1. A method of adjusting a voltage controlled oscillator (VCO), said method including steps of
 receiving an input directing said VCO to generate an output signal, said output signal having a programmable known output frequency, and an output amplitude within a known range; 
 first adjusting a first operating parameter of said VCO, said first operating parameter including said output amplitude, and determining an effect of said steps of first adjusting on at least two first operating parameters of said VCO, said at least two first operating parameters including said amplitude and frequency; 
 second adjusting a second operating parameter of said VCO, said second operating parameter including said output frequency, and determining an effect of said steps of second adjusting on at least two second operating parameters of said VCO, said at least two second operating parameters including said amplitude and frequency; and 
 repeatedly interleaving said steps of first adjusting and second adjusting, said steps of interleaving including performing one or more steps of delaying first and second adjusting until the VCO reaches an equilibrium state, said first adjusting in response to said second adjusting, and performing one or more steps of said second adjusting in response to said first adjusting; wherein said steps of repeatedly interleaving are performed until a known terminating condition. 
 
     
     
       2. A method as in  claim 1 , including steps of
 coupling said output signal to a peak detector, said peak detector providing an indicator of a extreme operating amplitude of said VCO, said extreme operating amplitude including at least a minimum or a maximum operating amplitude; and 
 in response to said output signal and said extreme operating amplitude, providing one or more control signals to the VCO, said control signals adjusting one or more said operating parameters, said operating parameters including a bias. 
 
     
     
       3. A method as in  claim 1 , wherein
 at least some times when said amplitude is adjusted, a first circuit determines whether said frequency should thereafter be adjusted; and 
 at least some times when said frequency is adjusted, a second circuit determines whether said amplitude should thereafter be adjusted. 
 
     
     
       4. A method as in  claim 1 , wherein
 said at least two first operating parameters, or said at least two second operating parameters, include one or more of: signal dropout or noise. 
 
     
     
       5. A method as in  claim 1 , wherein
 said steps of interleaving include performing said steps of first adjusting and second adjusting alternately. 
 
     
     
       6. A method as in  claim 1 , wherein
 said steps of interleaving include performing said steps of first adjusting and second adjusting alternately at a ratio of other than 1:1. 
 
     
     
       7. A method as in  claim 1 , wherein
 said steps of interleaving include performing said steps of first adjusting and second adjusting alternately in response to a random or pseudo-random process. 
 
     
     
       8. A method as in  claim 7 , wherein
 said random or pseudo-random process is disposed to average to a predetermined known ratio. 
 
     
     
       9. A method as in  claim 1 , wherein
 said VCO includes a switched capacitor array, said array being associated with one or more array bits; and 
 said settings are adjusted in an order having at least one of: a most significant bit (MSB) first, or a least significant bit (LSB) last. 
 
     
     
       10. A method as in  claim 1 , wherein
 said VCO includes a switched capacitor array, said array having one or more settings; and 
 at least some times when said settings are adjusted, a circuit determines whether at least one operating parameter of said VCO should be adjusted, said at least one operating parameter including said amplitude or frequency. 
 
     
     
       11. A method as in  claim 1 , wherein
 said steps of repeatedly interleaving are performed at least until one or more said operating parameters of said VCO are adjusted sufficiently that said VCO can be maintained at said known frequency by a selected circuit, said selected circuit including a phase locked loop (PLL). 
 
     
     
       12. A method as in  claim 1 , wherein
 said steps of repeatedly interleaving move a set of operating parameters of said VCO into a realm wherein a PLL can perform fine adjustment on said operating parameters to achieve a desired VCO operating frequency. 
 
     
     
       13. Apparatus including
 a voltage controlled oscillator (VCO), said VCO including a switched capacitor array; 
 a peak detector coupled to an output of said VCO, and disposed to provide a first signal, indicating one or more of: a VCO operating amplitude, a VCO operating frequency, another operating parameter of said VCO; 
 an automated level control (ALC) element coupled to said peak detector and to an input of said VCO, and disposed to provide a second signal, indicating one or more of: a bias applicable to said VCO, a target VCO operating amplitude; 
 a VCO coarse timing adjustment (VCTA) element coupled to said ALC and to an input of said VCO, and disposed to provide a third signal, indicating one or more of: a target VCO operating frequency, a target setting for a switched capacitor array; 
 a signal comparator coupled to a reference signal, an input of said VCTA, and an output of said VCO, and disposed to provide a fourth signal, indicating one or more of: a difference between said VCO operating frequency and a reference signal frequency, a target VCO operating frequency; 
 wherein said ALC element is responsive to said target VCO operating frequency to adjust said second signal, whereby the VCO operating amplitude is responsive to said target VCO operating frequency; 
 wherein said VCTA element is responsive to said target VCO operating amplitude to adjust said third signal, whereby the VCO operating frequency is responsive to said target VCO operating amplitude; and including 
 a delay element responsive to at least one of: the ALC element, the VCTA element, disposed to impose a delay between operation of the ALC element and the VCTA element until the VCO reaches an equilibrium state; and 
 a repeat element responsive to a known terminating condition, and disposed to cause the ALC element to operate in response to the VCTA element, and to cause the VCTA element to operate in response to the ALC element, while the known terminating condition has not yet occurred. 
 
     
     
       14. A apparatus as in  claim 13 , wherein
 said ALC element provides said second signal in response to said peak detector; and said second signal is operative to adjust a VCO operating amplitude. 
 
     
     
       15. A apparatus as in  claim 13 , wherein
 said second signal provided by said ALC is operative to maintain said VCO operating amplitude; such that a selected known threshold is greater than a sum of a bias and said VCO operating amplitude; wherein said known threshold is sufficiently low that downstream circuits are not damaged by an output of said VCO. 
 
     
     
       16. A apparatus as in  claim 13 , wherein
 said signal comparator includes 
 a first counter coupled to said reference signal; 
 a second counter coupled to an output from said VCO; and 
 a comparator coupled to said first counter and said second counter. 
 
     
     
       17. A apparatus as in  claim 13 , wherein
 said first signal provided by said peak detector is responsive to one or more of: a dropout of an output from said VCO; a noise parameter of an output from said VCO. 
 
     
     
       18. A apparatus as in  claim 13 , wherein
 said first signal provided by said peak detector is responsive to one or more of: a local maximum of an output from said VCO; a local minimum of an output from said VCO; another operating feature of an output from said VCO. 
 
     
     
       19. A apparatus as in  claim 13 , wherein
 said VCTA element is responsive to one or more instructions, directing said VCTA element to: 
 adjust said VCO operating amplitude, and receive information about operating parameters of an output from said VCO; 
 adjust said VCO operating frequency, and receive information about operating parameters of an output from said VCO; and 
 perform said instructions to adjust said VCO operating amplitude and said VCO operating frequency in an interleaved manner; 
 wherein said instructions to adjust said VCO operating amplitude and said VCO operating frequency in an interleaved manner move a set of operating parameters of said VCO into a realm wherein a PLL can perform fine adjustment on said operating parameters to achieve a desired VCO operating frequency. 
 
     
     
       20. A method, including steps of
 first adjusting an amplitude associated with an electronically-controlled device in response to a then-current frequency thereof; 
 second adjusting a frequency associated with the electronically-controlled device in response to a then-current amplitude thereof; 
 wherein said steps of first and second adjusting are delayed until the electronically-controlled device reaches an equilibrium state; 
 interleaving and repeating said steps of first adjusting and second adjusting; 
 whereby said steps of first adjusting and second adjusting are each applied a plurality of times until occurrence of a known terminating condition.